Light Test

Result

Light Test - 8

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Weekly Quiz Competition

Question 1
1 / -0

Two beams of light; one red and the other green fall on the same spot on a white screen. The colour on the screen will appear to be

A
magenta

B
blue

C
black

D
yellow

Solution

Red + Green = Yellow
Hence, (4)
Question 2
1 / -0

Which of the following statements is correct?

A
Ultraviolet rays play useful role in the production of vitamin A.

B
Ultraviolet rays are absorbed by ordinary glasses.

C
Only infrared rays can heat up the object on which it falls.

D
Violet rays has the lowest frequency among visible light.

Solution

Ultraviolet rays are absorbed by ordinary glasses.
Question 3
1 / -0

The totally dark part of the shadow is called

A
umbra

B
eclipse

C
penumbra

D
None of the above

Solution

The totally dark part of a shadow is called umbra.
Question 4
1 / -0

A picture seen on the screen of a pinhole camera is

A
an image

B
a shadow

C
neither an image nor a shadow

D
both an image and a shadow

Solution

A picture seen on the screen of a pinhole camera is an image.
Question 5
1 / -0

If a man approaches a plane mirror at the rate of 2 km/hr, then his image would approach him at the rate of

A
1 km/hr

B
2 km/hr

C
4 km/hr

D
8 km/hr

Solution

Given: Speed of the man (object) = 2 km/hr
Let's consider that the distance between the man and the plane mirror be 'x' km.
So, the distance between the man and his image will be '2x' km because the distance of image and object in case of the plane mirror is equal.
Thus, speed of the man = x/t = 2 km/hr
Then, speed of the image = 2x/t = 4 km/hr
Question 6
1 / -0

To see a full size image of ourselves, we should use a plane mirror of ____ times the height of ourselves.

A
3

B
2

C

D

Solution

To see the full size image of the man, the man needs a mirror with height of the height of the man.
Question 7
1 / -0

f = -R/2; this relation indicates that mirror is

A
plane

B
concave

C
convex

D
parabolic

Solution

f =
This relation indicates that the mirror is concave.
Question 8
1 / -0

A concave mirror of focal length f produces an image m times the size of the object. If the image is real, then the distance of the object from the mirror is

A
(m – 1)f

B

C

D
(m + 1)f

Solution

For the mirror

(for concave mirror all the distances are taken as negative)
Question 9
1 / -0

If refractive index for glass is 1.5, and the velocity of light in vacuum is 3.0 10⁸ m/sec, the time taken by the light in travelling a distance of 300 m in glass will be

A
1.4 10^-4 s

B
1.5 10^-5 s

C
1.5 10^-6s

D
1.5 10^-7s

Solution

1.5 = 3 × 10⁸/300 × t
t = 1.5 × 10^-6 sec
Question 10
1 / -0

When angle of incidence in a denser medium is equal to critical angle, the angle of refraction is

A
0^o

B
30^o

C
60^o

D
90^o

Solution

When angle of incidence in a denser medium is equal to critical angle, the angle of refraction is 90⁰
Question 11
1 / -0

We always get real image in a convex lens if the object is situated beyond

A
optical centre

B
focus

C
centre of curvature

D
None of the above

Solution

We always get real image in a convex lens if the object is situated beyond focus.
Question 12
1 / -0

An object is placed in front of a convex mirror between f and 2f. The image formed must be

A
real, inverted, and smaller in size

B
virtual, erect, and smaller in size

C
virtual, erect, and larger in size

D
real, inverted, and larger in size

Solution
Question 13
1 / -0

A ray of light strikes a thick parallel sided glass slab with an angle of incidence of 40°. The angle of the beam emerging from the other side of the slab with the normal is

A
40°

B
20°

C
60°

D
None of these

Solution

In the glass slab, angle of incidence = angle of emergence
A ray of light strikes a thick parallel sided glass slab with an angle of incidence of 40°. The angle of the beam emerging from the other side of the slab with the normal is 40°.
Question 14
1 / -0

When will the magnifying power of an astronomical telescope be increased?

A
If we increase the focal length of the objective

B
If we increase the focal length of the eyepiece

C
If we decrease the focal length of the objective

D
If we decrease the focal length of the objective and at the same time, increase the focal length of the eyepiece

Solution

Magnifying power of the telescope is given by:

If we increase the focal length of the objective, the magnifying power of an astronomical telescope will be increased.
Question 15
1 / -0

If f₀ and f_e are the focal lengths of the objective and eye – piece, respectively for a telescope, the magnifying power of the telescope will be

A
f₀/f_e

B
f₀ f_e

C
f_e/f₀

D
f₀ + f_e

Solution

If f₀ and f_e are the focal lengths of the objective and eye – piece, respectively for a telescope, the magnifying power of the telescope will be f_o/f_e
Question 16
1 / -0

Dispersion produced by a prism depends upon

A
size of the prism

B
its refracting index

C
height of the prism

D
one of the angles at the base of the prism

Solution

As the refractive index (μ) of the prism is different for different colors, therefore different colors deviate from different angles on passing through the prism. Hence, they are seen as separate. This is the cause of dispersion.
Question 17
1 / -0

Coloured band of light obtained by dispersion of white light is called

A
shadow

B
image

C
mirage

D
spectrum

Solution

Coloured band of light obtained by dispersion of white light is called spectrum.
Question 18
1 / -0

The sky appears blue because the earth's atmosphere

A
scatters blue light the most

B
transmits blue light

C
refracts blue light

D
refracts blue light more than the light of other colours

Solution

The sky appears blue because the earth's atmosphere scatters blue light the most.
Question 19
1 / -0

In a room, artificial rain is produced at one end and a strong source of white light is switched on at the other end. To observe the rainbow, an observer must

A
look anywhere in the room

B
look towards the sun

C
look towards the raindrops with his back towards the source of light

D
look in a direction equally inclined to the source of raindrops

Solution

In atmosphere, rainbow is observed when the observer looks towards the water droplets in the air after the rain with his back towards the sun. To observe the rainbow in the mentioned room, the observer must look towards the raindrops with his/her back towards the source of the white light.
Question 20
1 / -0

An eye specialist prescribes spectacles having a combination of convex lens of focal length 50 cm in contact with a concave lens of focal length 25 cm. The power of this combination of lenses (in dioptre) is

A
-2.5

B
-1.5

C
-0.04

D
-2.0

Solution

Power for convex lens = 100/50 = 2 D
Power for concave lens = -100/25 = -4 D
Total power = -4 D + 2 D = -2 D